This invention relates to a colour photographic silver halide material which exhibits improved granularity.
Colour photographic materials, particularly colour films, should have a granularity which is as fine as possible. However, since they should also have a high sensitivity to light, and increasing their sensitivity to light usually results in the enlargement of the silver halide grains which in turn has an adverse effect on granularity, it is often impossible to produce fine-grained colour photographic materials of high sensitivity.
Attempts have been made to overcome this disadvantage by employing certain benz-imidazoles (DE 195 07 913); however, this has resulted in an increase in fogging. 1-dodecyl-2-methylimidazole (U.S. Pat. No. 4,585,728, compound No. 18) exhibits what are merely unsatisfactory values of granularity and sensitivity.
The object of the present invention was to improve granularity without loss of sensitivity and without an increase in fogging.
It has now surprisingly been found that this object can be achieved by the addition of certain imidazoles.
The present invention therefore relates to a colour photographic silver halide material comprising a support and at least one silver halide emulsion layer which is deposited thereon and which contains at least one colour coupler, characterised in that said layer also contains a compound of formula (I) 
wherein
R1 denotes alkyl, aryl, aralkyl or hetaryl,
R2 denotes H or R1, or
R1 and R2 together denote the remaining members of a heterocyclic ring,
R3, R4, independently of each other, denote aryl or hetaryl or together denote the remaining members of a phenanthrene ring which is condensed-on in the 9,10-position,
wherein R1 can also be H if R3 and R4 together form a phenanthrene ring.
The aforementioned substituents can be substituted by halogen, hydroxy, alkoxy, amino, acylamino, alkoxycarbonyl and aininosulphonyl; aryl can be substituted by aralkyl in the aryl part, and hetaryl can also be substituted by alkyl.
In particular, the compound of formula (I) is used in the respective layer in an amount ranging from 0.1 to 3.0 mol, preferably 0.5 to 1.2 mol/mol coupler.
The compound of formula (I) is preferably dissolved or dispersed, together with the colour coupler, in a high-boiling organic solvent; the solution or dispersion is then emulsified in an aqueous solution of a binder, usually in an aqueous solution of gelatine.
The compound of formula (I) is preferably used together with a 2-equivalent magenta coupler of the pyrazolone series, which has a molecular weight between 500 and 1500 and is used in an amount of 0.3 to 1.5 g/m2.
Preferred pyrazolone couplers correspond to formula (II) 
wherein
R5 denotes a substituent from the series comprising aryl, alkylsulphoxyl, aryl-sulphoxyl, acyl, halogen, acylamino, aminosulphonyl, alkylsulphonyl, aryl-sulphonyl, sulphonamido, imido, carbamato, heteroacylyl, alkylthio, carboxyl or hydroxyl,
R6 denotes a substituent from the group comprising halogen, CN, allylsulphonyl, arylsulphonyl, sulphamoyl, sulphamido, carbamoyl, carbonamido, alkoxy, acyl-oxyl, aryloxy, alkoxycarbonyl, ureido, nitro, alkyl, perchloryl and trifluoro-methyl,
X denotes a cleavage group,
Y denotes a direct bond or CO, and
o and p denote 0 or a number from 1 to 5,
wherein if o and/or p greater than 1, the substituents R5 and R6 can be identical or different.
The preferred cleavage groups are halogen, alkoxy, aryloxy, alkylthio, arylthio, acyloxy, sulphonarnido, sulphonyloxy, carbonamido, arylazo, imido, heterocyclene radicals which contain nitrogen, and hetarylthio radicals.
Particularly preferred magenta couplers correspond to formula (III) 
wherein
R5 and R6 have the meanings given above,
R7 denotes hydrogen or an organic radical,
R8 denotes acylamino or sulphonylamino,
R9 denotes chlorine or a C1-C4 alkoxy group, and
r and q, independently of each other, denote 0, 1 or 2.
Suitable couplers of formulae (II) and (III) include: 
The compounds of formula I according to the invention can also be used in combination with yellow or cyan couplers and improve the sensitivity/granularity ratio there also.
The preferred compounds of formula (I) correspond to formulae (Ia) and (Ib) given below, wherein R1 and R2 have the meanings given above. 
Suitable compounds of formula (Ia):
Suitable compounds of formula (Ib):
The compounds according to the invention can be prepared by methods which are generally known. For example, they can be prepared as shown in Scheme 1 by the alkylation of a protic imidazole, or can be prepared in a particularly simple manner as shown in Scheme 2 by a multi-component reaction in which unsubstituted to tetra substituted imidazoles are obtained directly. 
Synthesis of Compound 3
A mixture of 212 g benzil, 268 g hexadecylamine, 25 g hexamethylenetetramine and 155 g ammonium acetate was stirred at 80xc2x0 C. for 4 hours in 500 ml glacial acetic acid. After cooling to room temperature, 1000 ml water and 1000 ml methanol were added and the batch was stirred for 2 hours.
The precipitate was filtered off and was washed successively with 2000 ml of a mixture of methanol/water (1:1), and then with 1500 ml methanol. Thereafter, the precipitate was stirred with 3000 ml methanol, filtered off and washed with 1500 ml methanol.
After drying, 309 g (69.5% theoretical) of compound 3 were obtained.
Examples of colour photographic materials include colour negative films, colour reversal films, colour positive films, colour photographic paper, colour reversal photographic paper, and colour-sensitive materials for the colour diffusion transfer process or the silver halide bleaching process.
Photographic materials consist of a support on which at least one light-sensitive silver halide emulsion layer is deposited. Thin films and foils are particularly suitable as supports. A review of support materials and of the auxiliary layers which are deposited on the front and back thereof is given in Research Disclosure 37254, Part 1 (1995), page 285 and in Research Disclosure 38957, Part XV (1996), page 627.
Colour photographic materials usually contain at least one red-sensitive, at least one green-sensitive and at least one blue-sensitive silver halide emulsion layer, and optionally contain intermediate layers and protective layers also.
Depending on the type of photographic material, these layers may be arranged differently. This will be illustrated for the most important products:
Colour photographic films such as colour negative films and colour reversal films comprise, in the following sequence on their support: 2 or 3 red-sensitive, cyan-coupling silver halide emulsion layers, 2 or 3 green-sensitive, magenta coupling silver halide emulsion layers, and 2 or 3 blue-sensitive, yellow-coupling silver halide emulsion layers. The layers of identical spectral sensitivity differ as regards their photographic speed, wherein the less sensitive partial layers are generally disposed nearer the support than are the more highly sensitive partial layers.
A yellow filter layer is usually provided between the green-sensitive and blue-sensitive layers, to prevent blue light from reaching the layers underneath.
The options for different layer arrangements and their effects on photographic properties are described in J. Inf. Rec. Mats., 1994, Vol. 22, pages 183-193, and in Research Disclosure 38957, Part M (1996), page 624.
Colour photographic paper, which as a rule is less sensitive to light than is colour photographic film, usually comprises the following layers on the support, in the following sequence: a blue-sensitive, yellow-coupling silver halide emulsion layer, a green-sensitive, magenta coupling silver halide emulsion layer, and a red-sensitive, cyan-coupling silver halide emulsion layer. The yellow filter layer can be omitted.
Departures from the number and arrangement of the light-sensitive layers may be effected in order to achieve defined results. For example, all the high-sensitivity layers may be combined to form a layer stack and all the low-sensitivity layers may be combined to form another layer stack in a photographic film, in order to increase the sensitivity (DE 25 30 645).
The essential constituents of the photographic emulsion layer are binders, the silver halide grains and colour couplers.
Information on suitable binders is given in Research Disclosure 37254, Part 2 (1995), page 286, and in Research Disclosure 38957, Part IIa (1996), page 598.
Information on suitable silver halide emulsions, their production, ripening, stabilisation and spectral sensitisation, including suitable spectral sensitisers is given in Research Disclosure 37254, Part 3 (1995), page 286, in Research Disclosure 37038, Part XV (1995), page 89, and in Research Disclosure 38957, Part VA (1996), page 603.
Photographic materials which exhibit camera-sensitivity usually contain silver bromide-iodide emulsions, which may also optionally contain small proportions of silver chloride. Photographic copier materials contain either silver chloride-bromide emulsions comprising up to 80 mole % AgBr, or silver chloride-bromide emulsions comprising more than 95 mole % AgCl.
Information on colour couplers is to be found in Research Disclosure 37254, Part 4 (1995), page 288, in Research Disclosure 37038, Part II (1995), page 80, and in Research Disclosure 38957, Part XB (1996), page 616. The maximum absorption of the dyes formed from the couplers and from the colour developer oxidation product preferably falls within the following ranges: yellow couplers 430 to 460 nm, magenta couplers 540 to 560 nm, cyan couplers 630 to 700 nm.
In order to improve sensitivity, granularity, sharpness and colour separation, compounds are frequently used in colour photographic films which on reaction with the developer oxidation product release compounds which are photographically active, e.g. DIR couplers, which release a development inhibitor.
Information on compounds such as these, particularly couplers, is to be found in Research Disclosure 37254, Part 5 (1995), page 290, in Research Disclosure 37038, Part XV (1995), page 86, and in Research Disclosure 38957, Part XC (1996), page 618.
The colour couplers, which are mostly hydrophobic, and other hydrophobic constituents of the layers also, are usually dissolved or dispersed in high-boiling organic solvents. These solutions or dispersions are then emulsified in an aqueous binder solution (usually a gelatine solution), and after the layers have been dried are present as fine droplets (0.05 to 0.8 xcexcm diameter) in the layers.
Suitable high-boiling organic solvents, methods of introduction into the layers of a photographic material, and other methods of introducing chemical compounds into photographic layers, are described in Research Disclosure 37254, Part 6 (1995), page 292.
The light-insensitive intermediate layers which are generally disposed between layers of different spectral sensitivity may contain media which prevent the unwanted diffusion of developer oxidation products from one light-sensitive layer into another light-sensitive layer which has a different spectral sensitivity.
Suitable compounds (white couplers, scavengers or DOP scavengers) are described in Research Disclosure 37254, Part 7 (1995), page 292, in Research Disclosure 37038, Part III (1995), page 84, and in Research Disclosure 38957, Part XD (1996), page 621 et seq.
The photographic material may additionally contain compounds which absorb UV light, brighteners, spacers, filter dyes, formalin scavengers, light stabilisers, anti-oxidants, DMin dyes, plasticisers (latices), biocides, additives for improving the dye-, coupler- and white stability and to reduce colour fogging and yellowing, and other substances. Suitable compounds are given in Research Disclosure 37254, Part 8 (1995), page 292, in Research Disclosure 37038, Parts IV, V, VI, VII, X, XI and XIII (1995), pages 84 et seq., and in Research Disclosure 38957, Parts VI, VIII, IX, X (1996), pages 607, 610 et seq.
The layers of colour photographic materials are usually hardened, i.e. the binder used, preferably gelatine, is crosslinked by suitable chemical methods.
Suitable hardener substances are described in Research Disclosure 37254, Part 9 (1995), page 294, in Research Disclosure 37038, Part XII (1995), page 86, and in Research Disclosure 38957, Part IIB (1996), page 599.
After image-by-image exposure, colour photographic materials are processed by different methods corresponding to their character. Details on the procedures used and the chemicals required therefor are published in Research Disclosure 37254, Part 10 (1995), page 294, in Research Disclosure 37038, Parts XVI to XXIII (1995), page 95 et seq., and in Research Disclosure 38957, Parts XVIII, XIX, XX (1996), together with examples of materials.